With the development of human civilization, greater number of electromechanical products is used. Various electromechanical products greatly enhance original functions of our movement, senses, and thinking. Moreover, with fast advancement of the world economy, different electromechanical products undergo increasingly fast updating, and many old electromechanical products are rapidly replaced by new products with better functions and higher performance to price ratio. Among these, automobiles and electronic devices are two types of products with the highest replacement speed and replacement rate.
Electronic devices comprise office automation devices, television receivers, computers, air conditioners, washing machines, refrigerators, computer motherboards, video recorders, mini sound devices, radios/recorders, vacuum cleaners, wind machines, mobile phones, electric heaters, and so on. Metal materials exist more or less all electronic devices, and realize certain electronic/electric functions, such as metal circuits in printed circuit boards, alone or in combination with rubber materials. However, a large number of waste metal materials generated by updating, repairing or failure of the electronic devices enter the environment, and have largely become waste.
There are many metal materials in automobiles. In one aspect, metal materials alone or in combination with rubber materials implement particular functions. In another aspect, people have increasingly high requirements for automobile performance such as safety, maneuverability, comfortableness and so on. Accordingly, automobiles have more and more electronic devices containing various metal materials.
If discarded automobiles and electronic waste are piled up in the open air or simply processed, metal waste will be converted into three types of wastes: liquid waste, gaseous waste, and solid waste. All of these are difficult for the environment to eliminate and generate secondary pollution and increasingly severe trouble.
If effective recycling and reusing can be performed on metal in wastes of automobiles and home appliances, environment burden or pollution will be greatly decreased or improved, and a new type of material resources will be formed.
Nowadays, a popular method for recycling metal wastes in automobiles and electronic devices employs separation and purification technologies. This recycling method is based on early industrial material concepts and traditional industrial processes, and is impeccable from a theoretical perspective since the purification technology of metal elements is more mature and easier to implement than a purification and separation technology of polymers.
However, with fast development of industrial facilities in urban and rural regions, problems occur regardless of whether a dry purification process or a wet purification process are used. For example, the dry purification process mainly employs high temperature melting, which is of high energy consumption, high treatment cost and non-neglectable heat pollution. Wet purification mainly employs strong acid and strong oxidant, which easily cause secondary pollution while extracting residual liquid and features bad operation condition in factories.
To summarize, since the traditional treatment methods cannot guarantee comparatively low treatment cost and good environmental benefit and cause bad treatment/utilization effect, high cost and poor scale benefit and industrial advantage, such methods are not beneficial to the society and commercial operation is difficult to be enhanced.
In this aspect, China Patent No. 02113059.0 discloses a method for recycling metal, such as platinum, palladium, rhodium and so on, from a waste catalyst of automobile exhaust. The method comprises steps of crushing the waste catalyst, dissolving it via inorganic acid, ion exchange, separating platinum via ammonium complex formation, extracting palladium via complexation, and separating rhodium with copper powder. It has been reported that this method has a simple technology and a high metal recycling rate: platinum recycling rate >96%, palladium recycling rate >97%, rhodium recycling rate >90%, product purity of platinum, palladium, and rhodium ≧99.95%.
However, the above-mentioned method has many disadvantages including secondary pollution of residual liquid, pool operation condition in factories, inability to enhance treatment, and so on.